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School children and their teacher peer from beneath a table during a state-wide air raid test in Newark, New Jersey, in 1952.

On Saturday, residents in Hawaii were sent into a panic when they received alerts on their mobile phones and televisions warning that a ballistic missile was on its way. The warning, which claimed "this is not a drill," quickly prompted officials to say minutes later that it was sent in error, but what should you do in case of a real nuclear attack?

Survivors of an immediate blast would be much better served by finding cover, NBC News reported. A car is better than the open air, while most houses are considerably safer than a car, particularly if there is room to hunker down in a basement.

“Go as far below ground as possible or in the center of a tall building,” says Ready.gov, the website created by FEMA and the Department of Homeland Security. “The goal is to put as many walls and as much concrete, brick and soil between you and the radioactive material outside.” The site recommends staying inside for at least 24 hours, unless authorities recommend coming out sooner.

The sheltering directives go against the basic human instinct to flee and to reunite with family members as quickly as possible, emergency preparedness officials acknowledge. But parents are directed to leave their kids in school or day care, rather than risk driving to them in the radiation-laden atmosphere.